sackchief does DQ reviews and good tidbit videos: https://www.youtube.com/user/Sackchief
GC Positive did some in depth reviews of the mainline series, but focuses on other games too: https://www.youtube.com/watch?v=kpeYa95mvKM&list=PLCGj9A7lAH8QQkkPMdLZOR1h2HXL0zmyZ
Mr Gentleman does some pretty good in depth DQ analysis videos (currently up to DQIV) https://www.youtube.com/channel/UCH0fH_3lhJtgHK3bsBFx3_Q
Geekdom101 is the biggest Dragon Ball Youtuber but also does some DQ stuff from time to time. He plans to review the episodes for the upcoming Dai Anime: https://www.youtube.com/channel/UCgIqhB8oD5SZ0yUSp71VCOQ
I started doing DQ material a year ago with a long in depth review of DQXI and this fall, I'll be releasing in-depth reviews of DQX and all it's expansions: https://www.youtube.com/channel/UCePtmyRFS1XrY_NEfMC5cQQ?disable_polymer=true
Here's my trailer for upcoming DQX reviews in October:
I'm surprised after all these years, DQ content is still relatively small on youtube, but there are quite a few dedicated people out there!